This invention relates to tufting machines and more particularly to a method and apparatus for increasing the density of the pile fabric produced even in fine gauge tufting machines, and further to a method and apparatus which permits not only the density of such fabric to be increased but patterning effects and streak break-up therein.
In the production of tufted fabrics a plurality of spaced yarn carrying needles extend transversely across the machine and are reciprocated cyclically to penetrate and insert pile into a backing material fed longitudinally beneath the needles. During each penetration of the backing material a row of pile is produced transversely across the backing. Successive penetrations result in a longitudinal row of pile produced by each needle. This basic method of tufting limits the aesthetic appearance of tufted fabrics so produced. Thus, the prior art has developed a number of procedures for initiating relative lateral movement between the backing material and the needles in order to laterally displace longitudinal rows of stitching and thereby create various pattern effects, to break up the unattractive alignment of the longitudinal rows of tufts and to reduce the affects of streaking which results from variations in coloration of the yarn.
One such procedure has been to jog or shift the needle bar transversely across the tufting machine relatively to the base material in a step-wise manner in accordance with a pattern. Exemplary of this prior art are U.S. Pat. Nos. 3,026,830; 3,964,408; 3,972,295; 4,010,700; 4,173,192; and 4,392,440.
It is also known to initiate relative movement between the backing material and the needles by jogging or shifting the needle plate, i.e., the plate over which the backing material is fed and which carries a plurality of fingers between which the needles extend during penetration. Examplary of this prior art are U.S. Pat. Nos. 3,301,205; 3,577,943; 3,934,524 and 3,964,407.
Another procedure for initiating relative lateral shifting between the needle and the backing material is by the use of what is known as a "jute shifter" wherein the gauge parts, i.e., needles etc. remain laterally stationary while the backing material alone is shifted usually by spike rollers upstream and/or downstream of the feed direction. However, when synthetic, as opposed to jute backing, was introduced, difficulties resulted since the synthetic backings are more difficult to shift than jute backings. The synthetic backings do not respond positively in every instance or uniformly to the movement of the rollers. Consequently, use of such "jute shifters" are not in favor at this time.
Another reason for initiating relative lateral movement between the needles and the backing material is to increase the density of the fabric by placing the stitches closer than the gauge of the machine, and in fact this was the main objective in a number of the aforesaid patents including U.S. Pat. Nos. 3,577,943 and 3,934,524. Another proposal for increasing the density of the pile fabrics produced by tufting was a proposal illustrated in U.S. Pat. No. 3,596,617 in which the loopers and cutting knives were proposed to be simultaneously shifted together with the needles and which was proposed at a time when relatively fine gauge tufting machines were not developed to a practical extent. However, this mechanism itself was found to be exeptionally complex and too impractical, and thus was never used in production.
When utilizing a sliding needle bar the needle bar drive pattern and the timing of the machine is generally such that the needles are laterally shifted while they are above the needle plate so as not to contact the needle plate fingers. In the prior art, before it was practical to produce a cam having a large peripheral surface, when it was desired to have a larger pattern repeat, i.e., more stitches within each repetition of the pattern, it was necessary to instigate lateral movement of the needle bar while the needles were still in the backing material and thereafter continue the lateral movement of the needle bar while the needles were free of the backing material to compensate for the small dwell time permitted by the prior art cams. Moreover, in the aforesaid U.S. Pat. No. 3,577,943 the backing material was shifted by the needle plate during a portion of the time that the needles were within and moving downwardly through the backing material to produce a dense cut pile fabric.
It has recently been proposed to intentionally shift the needle bar while the needles are within the fabric to move the fabric slightly and thereby increase the density. Obviously, an intentional jogging of the needles while within the base material must occur without the needles engaging the needle plate fingers to prevent breakage of the needles and/or the fingers.
It should be understood that each time the needles shift laterally they must at the time of loop seizure be in cooperative relationship with a corresponding looper. Thus, by jogging back and forth a greater density of tufts occurs at certain portions of the fabric than at others and this can be specifically seen in cut/loop fabrics. Consequently, merely by timing the needle shifting to occur in this manner precludes the use of such constructions in fine gauge tufting machines, e.g., one eighth inch and smaller between the respective gauge parts, and due to variations in density in the fabrics, even some coarser gauge fabrics, such as cut/loop, may be precluded. Thus, the amount of movement of the needles if any shifting within the fabric occurs in this manner is exeptionally limited and such increase in density can only be accomplished in certain coarser gauge machines where there is sufficient space between the needle plate fingers and where patterning will not be detrimentally effected. Thus, although shifting of the needles less than a full gauge has been accomplished in coarse gauges, a practical solution to increasing the density of fine gauge tufting machine products has not heretofore been proposed.